Interpretive Summary: The soil-inhabiting fungus Fusarium oxysporum f. sp. erythroxyli is being investigated for use as a mycoherbicide against the narcotic plant coca. When formulations of Fusarium were used in field tests, ants removed the formulation granules. Thus, ants may help to distribute the Fusarium within the soil profile and get it near the roots where it can cause infection. This work was undertaken to determine which formulations ants prefer and whether ants carried the Fusarium into the soil. Formulations with wheat flour were removed (90%) by ants within 24 h, while fewer formulation granules with rice were removed (20%). When canola, sunflower or olive oil were added to the rice formulation, 90% of the granules were removed within 24 h. Formulations with canola meal were less attractive (65% removed) than wheat flour or granules with oils. The presence or absence of the fungus in the formulation did not affect how many granules were removed. When formulations were amended with natural products, canna and tansy leaves greatly reduced removal of granules and these amendments did not harm the Fusarium. Chili powder also reduced the attractiveness to ants, but chili powder reduced viability of the Fusarium. Greater populations of the Fusarium were recovered from inside ant nests (3.5 inch depth) than from nest surfaces. Ants were also found to carry the mycoherbicidal fungus outside and inside their bodies. This information will be used by scientists developing F. o. erythroxyli for use against coca.

Technical Abstract:
Fusarium oxysporum f. sp. erythroxyli is being investigated for use as a mycoherbicide against the narcotic plant coca. During field trials in Kauai, HI, ants removed formulations of Fusarium from test plots. Preference of indigenous ants for removing formulations in HI was tested using three different food bases (rice, rice + canola oil, and wheat flour (gluten)). Similar tests were conducted at Beltsville, MD, using F. oxysporum f. sp. melonis where the wheat flour formulation was replaced by a canola meal formulation. Formulations based on wheat flour (C-6 and Pesta) were preferred by ants in both locations; 90% of the granules were removed within 24 h, while only 20% of those containing rice without oils were taken. However, when canola, sunflower or olive oil were added to the rice formulation, up to 90% of the granules were taken. Canola meal formulations were less attractive to ants (65% removed). Ants showed no preference with respect to presence or absence of fungal biomass. To alte the attractiveness of the C-6 formulation to ants, C-6 was amended with canna or tansy leaves (1:5, w:w), or chili powder (1:25 or 1:2.5, w:w). Canna, tansy and the higher rate of chili powder significantly reduced the number of C-6 granules removed by ants. Canna and tansy leaves did not affect viability of the Fusarium, while the high concentration of chili powder reduced viability. More F. oxysporum f. sp. erythroxyli-type colonies were recovered from inside ant nests (9 cm depth) than from nest surfaces, indicating that ants may distribute the mycoherbicide in the soil profile. Ants passively carried propagules of F. oxysporum f. sp. erythroxyli both inside and outside their bodies.